1. Field of the Invention
The present invention relates to an image processing method, device and system for allowing image data, such as a page layout created on an image processing terminal using an application, to be subject to image processing such that the image data can be outputted with a printer.
2. Description of the Related Art
Desktop Publishing (DTP) has increased in use and popularity with the progress of digitalization in the field of print processing. DTP system can create, process and edit an image on an image processing terminal, such as a personal computer or a workstation, using various applications to create a page layout. In a color electronic plate-making system (CEPS), a printing device creates film for exposing a printing plate based on the page layout, and directly writes on the printing plate so as to create a press plate for printing (CTP: Computer to Plate).
When proofing is performed prior to printing or the like using an actual press plate, the page layout is displayed on a monitor, and then printed out using a WYSIWYG function or the like with a print output device such as a laser printer or a page printer.
In the printing process using the press plate, when colors are overlapped and plate misalignment occurs, color drift of an image or gaps between colors appear on the printed material. Particularly when overlapping a foreground color on a knockout (unprinted area) in the shape of the foreground object, formed on a background, plate misalignment causes white gaps to appear on the edges of the knockout shape. In order to prevent this, a trapping process is executed.
The trapping process includes spreading the foreground object and choking the knockout shape. In the spread process, for example, when a circular object is overlapped on a square object, the inside of the square object is knocked out in the shape of the circular object, and the circular object is drawn so as to be larger than the original circular object. In the choke process, the inside of the square object is knocked out in the shape of the circular object such that the knocked out shape is smaller than the circular object, and the circular object is drawn in the original size.
As a result, in both the spreading and choking, trapping in which the periphery edge portion of the circular object is overprinted on the square object is realized.
In order to achieve overprinting using a color printer, separated output for data of individual colors such as cyan (C) magenta (M). yellow (Y) and black (B) is required, as is the case when creating a press plate. For this reason, respective separation plates must be synthesized and output by using an image processing device having a synthesizing function. However, synthesizing image data separated and outputted on the application side requires hardware having large memory capacity and high processing ability. Moreover, separation output requires longer processing time than composite output, wherein image data is outputted without separating color into C, M, Y and K.
A technique has been proposed in which the trapping process is carried out on a bit map image read by a layout scanner or the like (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2000-106628).
However, implementation of this technique has several drawbacks in that expensive hardware is required, and it is difficult to reproduce setting of trap width, choke and spread for each object set by an application.
Namely, in the composite output, the application outputs only a drawing code for executing a process (e.g., “drawing a square and a circle”), and this code does not include a drawing code in which the trapping is taken into consideration. For this reason, in order to reproduce the trapping by means of the composite output, it is necessary to knockout the object in which the trapping is set and to perform trapping before that object is drawn.
In a standard drawing command, a “path ” for describing a shape composed of a series of connected points, lines, and curved lines, and non-connected points, lines, and curved lines, is constructed, after which actual drawing is executed. At this time, there is no guarantee that the constructed path will definitely be drawn, and thus the path might be used for a clip (drawing area specification) or occasionally discarded. Therefore, when knocking out is executed at the time of constructing the path, if the purpose or use of the path is unknown, the possibility exists that a different or undesirable drawing result will be obtained.
For this reason, knocking out must be executed not at the time of path construction but rather at the actual drawing stage. However, it is difficult to obtain information, such as accurate coordinates, from the constructed path. Moreover, it is not easy to determine what object is being drawn. As a result, it is difficult to execute trapping processes such as knocking out the background into a slightly smaller shape than the foreground object, or to draw the foreground shape as slightly larger. In other words, it is difficult to reproduce trapping from the composite output. Accordingly, the conventional art produces results that are far from satisfactory and is thus in need of improvement.